Aluminium alloy multi-layered brazing sheet material for flux-free brazing

ABSTRACT

Described herein is an aluminium alloy multi-layered brazing sheet product for brazing in an inert-gas atmosphere without a flux that includes a core layer made of a 3xxx alloy that includes &lt;0.2 wt.% Mg, and that provides a covering clad layer that includes 2-6 wt.% Si on one or both sides of said 3xxx alloy core layer and a Al—Si brazing clad layer that includes 7-13 wt.% Si positioned between the 3xxx alloy core layer and the covering clad layer, wherein the covering clad layer has a thickness X 1  and the Al—Si brazing clad layer has a thickness X 2  and wherein X 2  ≥ 2X 1 . Also described herein is the use of an aluminium alloy multi-layered brazing sheet product in a flux-free controlled atmosphere brazing (CAB) operation to produce a heat exchanger apparatus.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to European PatentApplication No. 20180172.7, filed Jun. 16, 2020, the contents of whichare herein incorporated by reference in its entirety.

FIELD

Described herein is an aluminium alloy multi-layered brazing sheetproduct or material for brazing in an inert gas atmosphere without aflux (“CAB”), comprising a core layer made of a 3××× alloy and providedwith a covering clad layer on one or both sides of the core layer and anAl—Si brazing clad layer comprising 7-13 wt.% Si positioned between thecore layer and the covering clad layer. Also described herein is abrazed assembly manufactured in a brazing operation, the brazed assemblycomprising various components and at least one component being made fromthe aluminium alloy multi-layered brazing sheet material according tothis disclosure.

BACKGROUND

Substrates of aluminium or aluminium alloy in the form of sheet orextrusion, are used to make shaped or formed products. In some of theseprocesses, parts of (shaped) aluminium comprising substrates areinterconnected. One end of a substrate may be interconnected with theother end or one substrate may be assembled with one or more othersubstrates. This is commonly done by brazing. In a brazing process, abrazing filler metal or brazing alloy or a composition producing abrazing alloy upon heating is applied to at least one portion of thesubstrate to be brazed. After the substrate parts are assembled, theyare heated until the brazing filler metal or brazing alloy melts. Themelting point of the brazing material is lower than the melting point ofthe aluminium substrate or aluminium core sheet.

Brazing sheet products find wide applications in heat exchangers andother similar equipment. Conventional brazing products have a core ofrolled sheet, typically, but not exclusively an aluminium alloy of the3×××-series, having on at least one surface of the core sheet analuminium brazing clad layer (also known as an aluminium claddinglayer). The aluminium brazing clad layer is made of a 4×××-series alloycomprising silicon as its main alloying constituent in an amount in therange of 4-20 wt.%. The aluminium brazing clad layer may be coupled orbonded to the aluminium core alloy in various ways known in the art, forexample by means of roll bonding, cladding spray-forming orsemi-continuous or continuous casting processes.

These aluminium brazing clad layers have a liquidus temperaturetypically in the range of about 540-620° C. and below the solidustemperature of the aluminium core alloy. Most brazing is done attemperatures between 560° C. and 615° C.

SUMMARY

Covered embodiments of the present disclosure are defined by the claims,not this summary. This summary is a high-level overview of variousaspects of the present disclosure and introduces some of the conceptsthat are further described in the Detailed Description section below.This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used in isolationto determine the scope of the claimed subject matter. The subject mattershould be understood by reference to appropriate portions of the entirespecification, any or all drawings, and each claim.

Described herein is an aluminium alloy multi-layered brazing sheetproduct for brazing in an inert-gas atmosphere without a flux comprisinga core layer made of a 3××× alloy comprising <0.20 wt.% Mg, and providedwith a covering clad layer comprising 2 wt.% to 6 wt.% Si on one or bothsides of said 3××× alloy core layer and a Al—Si brazing clad layercomprising 7 wt.% to 13 wt.% Si positioned between the 3××× alloy corelayer and the covering clad layer, wherein the covering clad layer has athickness X₁ and the Al—Si brazing clad layer has a thickness X₂ andwherein X₂ ≥ 2X₁.

Optionally, the 3××× alloy core layer comprises up to 0.1% Mg.Optionally, the covering clad layer is Bi-free and Li-free. Optionally,the covering clad layer is Mg-free, Bi-free and Li-free, and comprises,in wt.%:

Si 2% to 6%, preferably 2.5% to 5%, more preferably 3.5% to 5.0%; Fe upto 0.5%; Mn up to 0.2%; Cu up to 0.1%; Zn up to 0.4%; Ti up to 0.1%;inevitable impurities, each <0.05%, total <0.15%, balance aluminium.

Optionally, the 3××× alloy core layer comprises, in wt.%,

-   0.5% to 1.8% Mn;-   <0.20% Mg;-   up to 1.1% Cu;-   up to 0.7% Si;-   up to 0.7% Fe;-   up to 0.3% Cr;-   up to 0.3% Sc;-   up to 0.3% Zr and/or V;-   up to 0.25% Ti;-   up to 1.7% Zn;-   unavoidable impurities each up to 0.05% and total up to 0.2%, and    balance aluminium.

Optionally, the 3××× alloy core layer has a Cu content up to 0.15%.Optionally, the 3××× alloy core layer has a Cu content in the range of0.15% to 1.1%, and preferably in the range of 0.20% to 0.9%. Optionally,the Al—Si brazing clad layer comprises, in wt.%,

Si 7%-13%, and preferably 10%-13%; Mg up to 0.5%, and preferably 0.02%to 0.5%; Fe up to 0.7%; Cu up to 0.3%; Mn up to 0.8%; Zn up to 2%; Bi upto 0.3%, and preferably 0.06% to 0.3%; Ti up to 0.25%; balance aluminiumand unavoidable impurities each <0.05%, total <0.2%.

Optionally, the multi-layered brazing sheet is surface treated with analkaline or acidic etchant before a brazing step. Optionally, thecovering clad layer has a thickness X₁ and the Al—Si brazing clad layerhas a thickness X₂ and wherein X₂ ≥ 2.5X₁, and preferably X₂ ≥ 3X₁.Optionally, at least one of the core layer, the Al—Si brazing cladlayer, or the covering clad layer comprises at least 0.05 wt.% Ti.

Also described herein is a process for the production of a braze heatexchanger, comprising the steps of providing at least one aluminiumalloy multi-layered brazing sheet product, such as the above-describedmulti-layered brazing sheet product, and preferably the multi-layeredbrazing sheet is surface treated with an alkaline or acidic etchantbefore a brazing step; and brazing in a flux-free controlled atmospherebrazing (CAB).

Also described herein is the use of an aluminium alloy multi-layeredbrazing sheet product, such as the above-described multi-layered brazingsheet product, in a flux-free controlled atmosphere brazing (CAB)operation to produce a heat exchanger apparatus.

Other objects and advantages of the present disclosure will be apparentfrom the following detailed description of non-limiting examples anddrawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a typical arrangement of an aluminium alloy multi-layeredbrazing sheet product according to the present disclosure.

FIG. 1B is another typical arrangement of an aluminium alloymulti-layered brazing sheet product according to the present disclosure.

FIG. 2 is an isometric view of a portion of a brazed heat exchangerassembly according to the present disclosure.

DETAILED DESCRIPTION

As will be appreciated herein below, except as otherwise indicated,aluminium alloy designations and temper designations refer to theAluminium Association designations in Aluminium Standards and Data andthe Registration Records, as published by the Aluminium Association in2019, and frequently updated, and are well known to the person skilledin the art. The temper designations are laid down in European standardEN515.

For any description of alloy compositions or preferred alloycompositions, all references to percentages are by weight percent unlessotherwise indicated.

The term “up to” and “up to about”, as employed herein, explicitlyincludes, but is not limited to, the possibility of zero weight-percentof the particular alloying element to which it refers. For example, upto about 0.3% Cr may include an aluminium alloy having no Cr.

As used herein, the meaning of “a,” “an,” or “the” includes singular andplural references unless the context clearly dictates otherwise.

As used herein, a plate generally has a thickness of greater than about15 mm. For example, a plate may refer to an aluminium product having athickness of greater than about 15 mm, greater than about 20 mm, greaterthan about 25 mm, greater than about 30 mm, greater than about 35 mm,greater than about 40 mm, greater than about 45 mm, greater than about50 mm, or greater than about 100 mm.

As used herein, a shate (also referred to as a sheet plate) generallyhas a thickness of from about 4 mm to about 15 mm. For example, a shatemay have a thickness of about 4 mm, about 5 mm, about 6 mm, about 7 mm,about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13mm, about 14 mm, or about 15 mm.

As used herein, a sheet generally refers to an aluminium product havinga thickness of less than about 4 mm. For example, a sheet may have athickness of less than about 4 mm, less than about 3 mm, less than about2 mm, less than about 1 mm, less than about 0.5 mm, less than about 0.3mm, or less than about 0.1 mm.

All ranges disclosed herein are to be understood to encompass any andall subranges subsumed therein. For example, a stated range of “1 to 10”should be considered to include any and all subranges between (andinclusive of) the minimum value of 1 and the maximum value of 10; thatis, all subranges beginning with a minimum value of 1 or more, e.g., 1to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10.

Provided herein is an improved brazing sheet product for brazing in aninert gas atmosphere without a flux.

Specifically, provided herein is an aluminium alloy multi-layeredbrazing sheet product for brazing in an inert-gas atmosphere without aflux, comprising a core layer made of a 3××× alloy comprising <0.20 wt.%Mg, and provided with a covering clad layer comprising 2-6 wt.% Si onone or both sides of said 3××× alloy core layer and a Al—Si brazing cladlayer comprising 7-13 wt.% Si positioned between the 3××× alloy corelayer and the covering clad layer, wherein the covering clad layer has athickness X₁ and the Al—Si brazing clad layer has a thickness X₂ andwherein X₂ ≥ 2X₁.

Optionally, at least one of the core layer, Al—Si brazing clad layer, orcovering clad layer includes Ti (e.g., at least 0.05 wt.% Ti or greaterthan 0.05 wt.% Ti). In other words, in some examples, Ti isintentionally added to at least one of the core layer, Al—Si brazingclad layer, or covering clad layer.

The 3××× alloy core layer comprises <0.20% Mg, preferably up to 0.1% Mg,and more preferably up to 0.05% Mg (e.g., from 0% to less than 0.20%,from 0.025% to less than 0.20%, from 0.05% to less than 0.20%, from0.075% to less than 0.20%, from 0.10% to less than 0.20%, from 0.125% toless than 0.20%, from 0.15% to less than 0.20%, or from 0.175% to lessthan 0.20%). Optionally, the Mg content of the core layer can be about0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%,about 0.07%, about 0.08%, about 0.09%, about 0.1%, about 0.11%, about0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%,about 0.18%, or about 0.19%.

In accordance with the present disclosure, it has been found that thethin covering layer has a liquidus temperature substantially higher thanthe liquidus temperature of the Al—Si brazing clad layer so that themolten brazing material during a subsequent brazing operation at atemperature above the liquidus temperature of the Al—Si alloy brazingclad layer and below the liquidus temperature of the thin covering cladlayer is to cause said Al—Si alloy brazing clad layer to melt down whilekeeping said thin covering clad layer partially solid to prevent or atleast limit oxidation of the brazing material being melted, and thencause the Al—Si alloy brazing material to seep, due to volumetricexpansion, through segregation portions of said thin covering clad layeronto a surface of said thin covering clad layer and spread over thesurface of said thin covering clad layer to form an emerging surfaceresulting in a brazed joint. The covering clad layer will eventuallydissolve into the molten filler material. A high difference in the Sicontent of the thin covering layer and the Al—Si brazing clad layer isto create a difference in liquidus temperature. If the difference in theSi content is too low the oxidation protection layer effect is too low,and Si will start to diffuse from the Al—Si brazing clad layer to thethin covering layer during the heat-up cycle to brazing temperature.

The Si content of the covering clad layer can be from about 2% to 6%(e.g., from 2.25% to 6%, from 2.5% to 6%, from 2.75% to 6%, from 3% to6%, from 3.25% to 6%, from 3.5% to 6%, from 3.75% to 6%, from 4% to 6%,from 4.25% to 6%, from 4.5% to 6%, from 4.75% to 6%, from 5% to 6%, from5.25% to 6%, from 5.5% to 6%, or from 5.75% to 6%). Optionally, the Sicontent of the covering clad layer can be about 2%, about 2.25%, about2.5%, about 2.75%, about 3%, about 3.25%, about 3.5%, about 3.75%, about4%, about 4.25%, about 4.5%, about 4.75%, about 5%, about 5.25%, about5.5%, about 5.75%, or about 6%.

The Si content of the brazing clad layer can be from about 7% to 13%(e.g., from 7.25% to 13%, from 7.5% to 13%, from 7.75% to 13%, from 8%to 13%, from 8.25% to 13%, from 8.5% to 13%, from 8.75% to 13%, from 9%to 13%, from 9.25% to 13%, from 9.5% to 13%, from 9.75% to 13%, from 10%to 13%, from 10.25% to 13%, from 10.5% to 13%, from 10.75% to 13%, from11% to 13%, from 11.25% to 13%, from 11.5% to 13%, from 11.75% to 13%,from 12% to 13%, from 12.25% to 13%, from 12.5% to 13%, or from 12.75%to 13%). Optionally, the Si content of the brazing clad layer can beabout 7%, about 7.25%, about 7.5%, about 7.75%, about 8%, about 8.25%,about 8.5%, about 8.75%, about 9%, about 9.25%, about 9.5%, about 9.75%,about 10%, about 10.25%, about 10.5%, about 10.75%, about 11%, about11.25%, about 11.5%, about 11.75%, about 12%, about 12.25%, about 12.5%,about 12.75% or about 13%.

An important advantage of having a low Mg content in the aluminium corealloy layer is the compatibility with this approach in CAB furnaces thatare also used with fluxed components in a heat exchanger to be brazed.There is no need for separate equipment for flux-free brazing. The Mgcontent in the aluminium core alloy can be from 0% to 0.2% (e.g., from0.025% to 0.2%, from 0.05% to 0.2%, from 0.075% to 0.2%, from 0.1% to0.2%, from 0.125% to 0.2%, from 0.150% to 0.2%, or from 0.175% to 0.2%).Optionally, the Mg content of the aluminium core alloy can be about0.025%, about 0.05%, about 0.075%, about 0.1%, about 0.125%, about0.150%, about 0.175%, or about 0.2%.

In an embodiment, the aluminium core alloy layer is made from a3XXX-series aluminium alloy consisting of, in wt.%:

-   0.5% to 1.8% Mn, preferably 0.6% to 1.5%, and more preferably 0.8%    to 1.3%;-   < 0.20% Mg, preferably up to 0.1%, and more preferably up to 0.05%;-   up to 1.1% Cu, and preferably up to 0.15% or alternatively in a    range of 0.15% to 1.1%, and preferably 0.20% to 0.95%, and more    preferably 0.20% to 0.60%;-   up to 0.7% Si, and preferably up to 0.3% or alternatively in a range    of 0.3% to 0.7% and more preferably of 0.40% to 0.65%;-   up to 0.7% Fe, preferably up to 0.5%, and more preferably in a range    of 0.05% to 0.35%;-   up to 0.3% Cr, preferably up to 0.20%, and more preferably up to    0.09%, and most preferably up to 0.04%;-   up to 0.3% Sc, preferably up to 0.25%;-   up to 0.3% Zr and/or V, preferably up to 0.09%, and more preferably    up to 0.04%;-   up to 0.25% Ti, preferably 0.01% to 0.20%, more preferably 0.01% to    0.12%;-   up to 1.7% Zn, preferably up to 1.2% Zn, more preferably up to 0.5%,    and most preferably up to 0.2%;-   balance aluminium and impurities. Typically impurities are each up    to 0.05% maximum and in total 0.2% maximum, and preferably in total    not exceeding 0.15%.

The Mn content in the aluminium core alloy layer can be from 0.5% to1.8% (e.g., from 0.6% to 1.5%, or from 0.8% to 1.3%). Optionally, the Mncontent in the aluminium core alloy layer can be about 0.5%, about0.55%, about 0.6%, about 0.65%, about 0.7%, about 0.75%, about 0.8%,about 0.85%, about 0.9%, about 0.95%, about 1%, about 1.05%, about 1.1%,about 1.15%, about 1.2%, about 1.25%, about 1.3%, about 1.35%, about1.4%, about 1.45%, about 1.5%, about 1.55%, about 1.6%, about 1.65%,about 1.7%, about 1.75%, or about 1.8%.

The Mg content of the aluminium core alloy layer can be from 0% to lessthan 0.20% (e.g., from 0.02% to less than 0.20%, from 0.04% to less than0.20%, from 0.06% to less than 0.20%, from 0.08% to less than 0.20%,from 0.10% to less than 0.20%, from 0.12% to less than 0.20%, from 0.14%to less than 0.20%, from 0.16% to less than 0.20%, or from 0.18% to lessthan 0.20%). Optionally, the Mg content of the aluminium core alloylayer can be about 0.01%, about 0.02%, about 0.03%, about 0.04%, about0.05%, about 0.06%, about 0.07%, about 0.08%, about 0.09%, about 0.10%,about 0.11%, about 0.12%, about 0.13%, about 0.14%, about 0.15%, about0.16%, about 0.17%, about 0.18%, or about 0.19%.

The Cu content of the aluminium core alloy layer can be from 0% to 1.10%(e.g., from 0.15% to 1.1%, from 0.20% to 0.95%, or from 0.20% to 0.60%).Optionally, the Cu content of the aluminium core alloy layer can be 0%,about 0.05%, about 0.10%, about 0.15%, about 0.20%, about 0.25%, about0.30%, about 0.35%, about 0.40%, about 0.45%, about 0.50%, about 0.55%,about 0.60%, about 0.65%, about 0.70%, about 0.75%, about 0.80%, about0.85%, about 0.90%, about 0.95%, about 1.00%, about 1.05%, or about1.10%.

The Si content of the aluminium core alloy layer can be from 0% to 0.7%(e.g., from 0.1% to 0.7%, from 0.2% to 0.7%, from 0.3% to 0.7%, from0.4% to 0.7%, from 0.5% to 0.7%, from 0.6% to 0.7%, from 0% to 0.3%, orfrom 0.4% to 0.65%). Optionally, the Si content of the aluminium corealloy layer can be 0%, about 0.025%, about 0.05%, about 0.075%, about0.10%, about 0.125%, about 0.15%, about 0.175%, about 0.20%, about0.225%, about 0.25%, about 0.275%, about 0.30%, about 0.325%, about0.35%, about 0.375%, about 0.40%, about 0.425%, about 0.45%, about0.475%, about 0.50%, about 0.525%, about 0.55%, about 0.575%, about0.60%, about 0.625%, about 0.65%, about 0.675%, or about 0.70%.

The Fe content of the aluminium core alloy layer can be from 0% to 0.7%(e.g., from 0.1% to 0.7%, from 0.2% to 0.7%, from 0.3% to 0.7%, from0.4% to 0.7%, from 0.5% to 0.7%, from 0.6% to 0.7%, from 0% to 0.50%, orfrom 0.05% to 0.35%). Optionally, the Fe content of the aluminium corealloy layer can be 0%, about 0.025%, about 0.05%, about 0.075%, about0.10%, about 0.125%, about 0.15%, about 0.175%, about 0.20%, about0.225%, about 0.25%, about 0.275%, about 0.30%, about 0.325%, about0.35%, about 0.375%, about 0.40%, about 0.425%, about 0.45%, about0.475%, about 0.50%, about 0.525%, about 0.55%, about 0.575%, about0.60%, about 0.625%, about 0.65%, about 0.675%, or about 0.70%.

The Cr content of the aluminium core alloy layer can be from 0% to 0.30%(e.g., from 0.05% to 0.30%, from 0.10% to 0.30%, from 0.15% to 0.30%,from 0.20% to 0.30%, from 0.25% to 0.30%, from 0% to 0.20%, from 0% to0.09%, or from 0% to 0.04%). The Cr content of the aluminium core alloylayer can be 0%, about 0.025%, about 0.05%, about 0.075%, about 0.10%,about 0.125%, about 0.15%, about 0.175%, about 0.20%, about 0.225%,about 0.25%, about 0.275%, or about 0.30%.

The Sc content of the aluminium core alloy layer can be from 0% to 0.30%(e.g., from 0.05% to 0.30%, from 0.10% to 0.30%, from 0.15% to 0.30%,from 0.20% to 0.30%, from 0.25% to 0.30%, or from 0% to 0.25%).Optionally, the Sc content of the aluminium core alloy layer can be 0%,about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about0.06%, about 0.07%, about 0.08%, about 0.09%, about 0.10%, about 0.11%,about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about0.17%, about 0.18%, about 0.19%, about 0.20%, about 0.21%, about 0.22%,about 0.23%, about 0.24%, about 0.25%, about 0.26%, about 0.27%, about0.28%, about 0.29%, or about 0.30%.

The Zr and/or V content of the aluminium core alloy layer can each befrom 0% to 0.30% (e.g., from 0.05% to 0.30%, from 0.10% to 0.30%, from0.15% to 0.30%, from 0.20% to 0.30%, from 0.25% to 0.30%, from 0% to0.09%, or from 0% to 0.04%). Optionally, the Zr and/or V content of thealuminium core alloy layer can be 0%, about 0.01%, about 0.02%, about0.03%, about 0.04%, about 0.05%, about 0.06%, about 0.07%, about 0.08%,about 0.09%, about 0.10%, about 0.11%, about 0.12%, about 0.13%, about0.14%, about 0.15%, about 0.16%, about 0.17%, about 0.18%, about 0.19%,about 0.20%, about 0.21%, about 0.22%, about 0.23%, about 0.24%, about0.25%, about 0.26%, about 0.27%, about 0.28%, about 0.29%, or about0.30%.

The Ti content of the aluminium core alloy layer can be from 0% to 0.25%(e.g., from 0.05% to 0.25%, from 0.10% to 0.25%, from 0.15% to 0.25%,from 0.20% to 0.25%, from 0.01% to 0.20%, or from 0.01% to 0.12%).Optionally, the Ti content of the aluminium core alloy layer can be 0%,about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about0.06%, about 0.07%, about 0.08%, about 0.09%, about 0.10%, about 0.11%,about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about0.17%, about 0.18%, about 0.19%, about 0.20%, about 0.21%, about 0.22%,about 0.23%, about 0.24%, or about 0.25%.

The Zn content of the aluminium core alloy layer can be from 0% to 1.7%(e.g., from 0.25% to 1.7%, from 0.50% to 1.7%, from 0.75% to 1.7%, from1.0% to 1.7%, from 1.25% to 1.7%, from 1.5% to 1.7%, from 0% to 1.2%,from 0% to 0.50%, or from 0% to 0.20%). Optionally, the Zn content ofthe aluminium core alloy layer can be 0%, about 0.05%, about 0.10%,about 0.15%, about 0.20%, about 0.25%, about 0.30%, about 0.35%, about0.40%, about 0.45%, about 0.50%, about 0.55%, about 0.60%, about 0.65%,about 0.70%, about 0.75%, about 0.80%, about 0.85%, about 0.90%, about0.95%, about 1.00%, about 1.05%, about 1.10%, about 1.15%, about 1.20%,about 1.25%, about 1.30%, about 1.35%, about 1.40%, about 1.45%, about1.50%, about 1.55%, about 1.60%, about 1.65%, or about 1.70%.

In an embodiment, the covering clad layer is free of wetting elements orelements modifying the surface tension of a molten Al—Si alloy, selectedfrom the group of Ag, Be, Bi, Ca, Ce, La, Li, Na, Pb, Se, Sb, Sr, Th,and Y. With “free” is meant that no purposeful addition of Ag, Be, Bi,Ca, Ce, La, Li, Na, Pb, Se, Sb, Sr, Th, or Y is made to the chemicalcomposition but that due to impurities and/or leaking from contact withmanufacturing equipment, trace quantities of may nevertheless find theirway into the covering material layer. In practice this means that theamount present of each of these defined elements, if present, is up toabout 0.005%, typically less than about 0.001%. In an embodiment the sumof these wetting elements does not exceed 0.01%, and preferably does notexceed 0.005%. For example, less than 10 ppm Sr, and preferably lessthan 5 ppm Sr, is an example of a trace quantity. Also, less than 10 ppmNa, and preferably less than 3 ppm Na is another example of a tracequantity. The avoidance of wetting elements, for example an element likeBi, is important as it reduces the occurrence of edge cracking duringliner production. The presence of wetting elements would limit also thepositive effect of preventing the surface from reoxidation duringbrazing by having a partially melted covering clad or top layer as itmight flow too easy should a wetting element be present.

The covering clad layer is preferably free from Mg, meaning that thelevel is below about 0.05%, preferably below about 0.03%, and morepreferably below 0.01%. With “free” is meant that no purposeful additionof Mg is made to the chemical composition but that due to impuritiesand/or leaking from contact with manufacturing equipment, tracequantities of may nevertheless find their way into the covering materiallayer.

In an embodiment, the covering clad layer is a Mg-free aluminium alloyand comprising, in wt.%,

Si 2% to 6%, preferably 2.5% to 5%, more preferably 3.5% to 5.0%; Fe upto 0.5%, preferably up to 0.3%; Mn up to 0.2%, preferably up to 0.10%;Cu up to 0.1%, preferably up to 0.05%; Zn up to 0.4%, preferably up to0.2%; Ti up to 0.1%, preferably up to 0.05%; inevitable impurities, each<0.05%, total <0.15%, and preferably each <0.02% and total <0.05%,balance aluminium.

The Si content of the covering clad layer can be from 2% to 6% (e.g.,from 2.5% to 6%, from 3% to 6%, from 3.5% to 6%, from 4% to 6%, from4.5% to 6%, from 5% to 6%, from 5.5% to 6%, from 2.5% to 5%, or from3.5% to 5%). Optionally, the Si content of the covering clad layer canbe about 2%, about 2.25%, about 2.5%, about 2.75%, about 3%, about3.25%, about 3.5%, about 3.75%, about 4%, about 4.25%, about 4.5%, about4.75%, about 5%, about 5.25%, about 5.75%, or about 6%.

The Fe content of the covering clad layer can be from 0% to 0.5% (e.g.,from 0.1% to 0.5%, from 0.2% to 0.5%, from 0.3% to 0.5%, from 0.4% to0.5%, or from 0% to 0.3%). Optionally, the Fe content of the coveringclad layer can be 0%, about 0.025%, about 0.05%, about 0.075%, about0.1%, about 0.125%, about 0.15%, about 0.175%, about 0.2%, about 0.225%,about 0.25%, about 0.275%, about 0.3%, about 0.325%, about 0.35%, about0.375%, about 0.4%, about 0.425%, about 0.45%, about 0.475%, or about0.5%.

The Mn content of the covering clad layer can be from 0% to 0.2% (e.g.,from 0.05% to 0.2%, from 0.1% to 0.2%, from 0.15% to 0.2%, or from 0% to0.1%). Optionally, the Mn content of the covering clad layer can be 0%,about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about0.06%, about 0.07%, about 0.08%, about 0.09%, about 0.10%, about 0.11%,about 0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about0.17%, about 0.18%, about 0.19%, or about 0.20%.

The Cu content of the covering clad layer can be from 0% to 0.10% (e.g.,from 0.025% to 0.10%, from 0.05% to 0.10%, from 0.075% to 0.10%, or from0% to 0.05%). Optionally, the Cu content of the covering clad layer canbe 0%, about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%,about 0.06%, about 0.07%, about 0.08%, about 0.09%, or about 0.10%.

The Zn content of the covering clad layer can be from 0% to 0.40% (e.g.,from 0.05% to 0.40%, from 0.10% to 0.40%, from 0.15% to 0.40%, from0.20% to 0.40%, from 0.25% to 0.40%, from 0.30% to 0.40%, from 0.35% to0.40%, or from 0% to 0.20%). Optionally, the Zn content of the coveringclad layer can be 0%, about 0.02%, about 0.04%, about 0.06%, about0.08%, about 0.10%, about 0.12%, about 0.14%, about 0.16%, about 0.18%,about 0.20%, about 0.22%, about 0.24%, about 0.26%, about 0.28%, about0.30%, about 0.32%, about 0.34%, about 0.36%, about 0.38%, or about0.40%.

The Ti content of the covering clad layer can be from 0% to 0.10% (e.g.,from 0.025% to 0.10%, from 0.05% to 0.10%, from 0.075% to 0.10%, or from0% to 0.05%). Optionally, the Ti content of the covering clad layer canbe 0%, about 0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%,about 0.06%, about 0.07%, about 0.08%, about 0.09%, or about 0.10%.

In an embodiment the covering clad layer is a Mg-free aluminium alloyconsisting of, in wt.%, Si 2% to 6%, Fe up to 0.5%, Mn up to 0.2%, Cu upto 0.1%, Zn up to 0.4%, Ti up to 0.1%, inevitable impurities, each<0.05% and total <0.15%, balance aluminium, and with preferred narrowerranges as herein described and claimed.

In an embodiment of the present disclosure, the Al—Si brazing clad layerhas the following composition, comprising of, in wt.%,

-   Si 7%-13%, preferably 10%-13%, more preferably 11%-13%;-   Mg up to 0.5%, preferably 0.02% to 0.5%, and more preferably 0.02%    to 0.3%, and most preferably 0.10% to 0.20%;-   Fe up to 0.7%, preferably up to 0.5%;-   Cu up to 0.3%, preferably up to 0.1%;-   Mn up to 0.8%, preferably up to 0.2%;-   Zn up to 2%, preferably up to 0.3%;-   Ti up to 0.25%, preferably up to 0.15%, and more preferably up to    0.1%;-   balance aluminium, and unavoidable impurities each <0.05%, total    <0.2%.

The Si content of the Al—Si brazing clad layer can be from 7% to 13%(e.g., from 8% to 13%, from 9% to 13%, from 10% to 13%, from 11% to 13%,or from 12% to 13%). Optionally, the Si content of the brazing cladlayer can be about 7%, about 7.25%, about 7.5%, about 7.75%, about 8%,about 8.25%, about 8.5%, about 8.75%, about 9%, about 9.25%, about 9.5%,about 9.75%, about 10%, about 10.25%, about 10.5%, about 10.75%, about11%, about 11.25%, about 11.5%, about 11.75%, about 12%, about 12.25%,about 12.5%, about 12.75%, or about 13%.

The Mg content of the Al—Si brazing clad layer can be from 0% to 0.5%(e.g., from 0.02% to 0.5%, from 0.02% to 0.3%, or from 0.1% to 0.2%).Optionally, the Mg content of the brazing clad layer can be about 0.02%,about 0.04%, about 0.06%, about 0.08%, about 0.1%, about 0.12%, about0.14%, about 0.16%, about 0.18%, about 0.2%, about 0.22%, about 0.24%,about 0.26%, about 0.28%, about 0.3%, about 0.32%, about 0.34%, about0.36%, about 0.38%, about 0.4%, about 0.42%, about 0.44%, about 0.46%,about 0.48%, or about 0.5%.

The Fe content of the Al—Si brazing clad layer can be from 0% to 0.7%(e.g., from 0.1% to 0.7%, from 0.2% to 0.7%, from 0.3% to 0.7%, from0.4% to 0.7%, from 0.5% to 0.7%, from 0.6% to 0.7%, or from 0% to 0.5%).Optionally, the Fe content of the brazing clad layer can be about0.025%, about 0.05%, about 0.075%, about 0.1%, about 0.125%, about0.15%, about 0.175%, about 0.2%, about 0.225%, about 0.25%, about0.275%, about 0.3%, about 0.325%, about 0.35%, about 0.375%, about 0.4%,about 0.425%, about 0.45%, about 0.475%, about 0.5%, about 0.525%, about0.55%, about 0.575%, or about 0.6%, about 0.625%, about 0.65%, about0.675%, or about 0.7%.

The Cu content of the Al—Si brazing clad layer can be from 0% to 0.30%(e.g., from 0.05% to 0.30%, from 0.10% to 0.30%, from 0.15% to 0.30%,from 0.20% to 0.30%, from 0.25% to 0.30%, or from 0% to 0.10%).Optionally, the Cu content of the brazing clad layer can be 0%, about0.01%, about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%,about 0.07%, about 0.08%, about 0.09%, about 0.10%, about 0.11%, about0.12%, about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%,about 0.18%, about 0.19%, about 0.20%, about 0.21%, about 0.22%, about0.23%, about 0.24%, about 0.25%, about 0.26%, about 0.27%, about 0.28%,about 0.29%, or about 0.30%.

The Mn content of the Al—Si brazing clad layer can be from 0% to 0.80%(e.g., from 0.10% to 0.80%, from 0.20% to 0.80%, from 0.30% to 0.80%,from 0.40% to 0.80%, from 0.50% to 0.80%, from 0.60% to 0.80%, from0.70% to 0.80%, or from 0% to 0.20%). Optionally, the Mn content of thebrazing clad layer can be 0%, about 0.05%, about 0.10%, about 0.15%,about 0.20%, about 0.25%, about 0.30%, about 0.35%, about 0.40%, about0.45%, about 0.50%, about 0.55%, about 0.60%, about 0.65%, about 0.70%,about 0.75%, or about 0.80%.

The Zn content of the Al—Si brazing clad layer can be from 0% to 2%(e.g., from 0.25% to 2%, from 0.50% to 2%, from 0.75% to 2%, from 1.25%to 2%, from 1.5% to 2%, from 1.75% to 2%, or from 0% to 0.30%).Optionally, the Zn content of the brazing clad layer can be 0%, about0.20%, about 0.30%, about 0.40%, about 0.60%, about 0.80%, about 1.0%,about 1.2%, about 1.4%, about 1.6%, about 1.8%, or about 2.0%.

The Ti content of the Al—Si brazing clad layer can be from 0% to 0.25%(e.g., from 0.05% to 0.25%, from 0.10% to 0.25%, from 0.15% to 0.25%,from 0.20% to 0.25%, from 0% to 0.15%, or from 0% to 0.10%). Optionally,the Ti content of the aluminium core alloy layer can be 0%, about 0.01%,about 0.02%, about 0.03%, about 0.04%, about 0.05%, about 0.06%, about0.07%, about 0.08%, about 0.09%, about 0.10%, about 0.11%, about 0.12%,about 0.13%, about 0.14%, about 0.15%, about 0.16%, about 0.17%, about0.18%, about 0.19%, about 0.20%, about 0.21%, about 0.22%, about 0.23%,about 0.24%, or about 0.25%.

In a particular embodiment the Al—Si brazing clad layer may furthercomprise up to 0.3% Bi, preferably 0.06% to 0.3%, more preferably 0.11%to 0.20%, to facilitate the flow of the Al—Si brazing clad layer and toenhance joint formation during brazing.

In an embodiment of the present disclosure, the Al—Si brazing clad layerhas the following composition, consisting of, in wt.%,

-   Si 7%-13%, preferably 10%-13%, more preferably 11%-13%;-   Mg up to 0.5%, preferably 0.02% to 0.5%, and more preferably 0.02%    to 0.3%, and most preferably 0.10% to 0.20%;-   Fe up to 0.7%, preferably up to 0.5%;-   Cu up to 0.3%, preferably up to 0.1 %;-   Mn up to 0.8%, preferably up to 0.2%;-   Zn up to 2%, preferably up to 0.3%;-   Bi up to 0.3%, preferably 0.06% to 0.3%, more preferably 0.11% to    0.20%;-   Ti up to 0.25%, preferably up to 0.15%, and more preferably up to    0.1%;-   balance aluminium, and unavoidable impurities each <0.05%, total    <0.2%.

In an embodiment of the aluminium alloy multi-layered brazing sheetmaterial according to the present disclosure the 3××× alloy core layeris provided on both sides with the covering clad layer and the Al—Sibrazing clad layer. When both sides of the 3××× alloy core layer areclad in the same manner, the brazing sheet material consists of afive-layer configuration.

In an embodiment the aluminium alloy multi-layered brazing sheetmaterial is devoid of or free from of an aluminium alloy layerinterposed between the 3××× alloy core layer and the Al—Si brazing cladlayer as this would reduce the production yield giving raise theincreased product costs.

The aluminium alloy multi-layered brazing sheet material according topresent disclosure can be manufactured via various techniques. Forexample by means of roll bonding as is well known in the art, and whichmethod is preferred. The process may generally comprise the followingsteps:

-   casting the different aluminium alloys to obtain rolling blocks;-   scalping of the blocks on either side to remove surface segregation    zones originating from the casting process and to improve product    flatness;-   preheating of the brazing material blocks at 400° C. to 550° C.;-   hot rolling of the blocks forming the covering layer and the Al—Si    brazing clad layer until the desired thickness to provide multiple    hot rolled clad liners;-   alternatively hot rolling the blocks of the covering layer and the    Al—Si brazing clad layer to intermediate thickness and stacking the    two materials at intermediate thickness and further hot rolling the    stack to provide a hot rolled clad liner of required thickness    composed of the two layers;-   optionally homogenizing the aluminium core alloy block at 500° C. to    630° C. for at least 1 hour, preferably 1 to 20 hours;-   assembling the core alloy block with at least on one face,    optionally on both faces, the rolled clad liner(s) to obtain a    sandwich;-   preheating the sandwich at 400° C. to 550° C.;-   hot rolling the sandwich until an intermediate thickness, for    example 2 to 10 mm; cold rolling the hot rolled sandwich until the    desired final thickness to obtain a multi-layered brazing sheet    product; and-   optionally annealing at 200° C. to 480° C. to obtain a multi-layered    brazing sheet product of the desired temper, for example O-temper,    H2x-temper or H3x-temper.

Alternatively, on a less preferred basis, one or more of the coveringclad layer and the Al—Si brazing clad layer can be applied onto the 3×××alloy core layer by means of thermal spraying techniques. Oralternatively, the core aluminium alloy layer and the Al—Si alloybrazing clad layer can be manufactured by means of casting techniques,for example as disclosed in patent document WO-2004/112992, where afterthe covering clad layer can be applied by means of for example rollbonding or thermal spraying techniques.

In an embodiment the aluminium alloy multi-layered brazing sheetmaterial thus obtained is treated with an alkaline or acidic etchantbefore the brazing process to remove a surface oxide film to facilitatethe fluxless CAB brazing operation.

Preferably, the outer-surface of the aluminium alloy multi-layeredbrazing sheet material is treated with an acidic etchant. The acidicetchant preferably comprises 10 g/L to 25 g/L, more preferably 12 g/L to16 g/L, for example 14 g/L of H₂SO₄ and 0.5 g/L to 5 g/L, morepreferably 1 g/L to 3 g/L, for example 2 g/L of HF (5%). The acidicetchant may comprise at least one of the following mineral acids: H₂SO₄,H₃PO₄, HCl, HF and/or HNO3. Preferably, the acidic etchant is a mixtureof H₂SO₄ and HF. The acidic etchant is generally in the form of asolution and the mineral acid content is generally from 0.5 to 20 wt.%.

According to another embodiment the etchant may be alkaline. Thealkaline etchant may comprise at least one of the following: NaOH and/orKOH. The alkaline etchant is generally in the form of a solution and thealkaline content is generally from 0.5 to 20 wt.%. The alkaline etchantmay further comprise surfactants (for example, anionic surfactants suchas alkylbenzene sulfonates, alkyl sulfates, alkyl ether sulfates;cationic surfactants such as mono alkyl quaternary systems; non-ionicsurfactants such as with ester, ether or amide bonding (for exampleglycol esters); or amphoteric surfactants such as imidazolinederivatives or polypeptides) or complexing agents (for example sodiumgluconate, sorbitol, mucic acid or Arabic gum).

The alkaline etchant generally needs to be rinsed with an acid, forexample nitric or sulfuric acid.

The surface treatment with an etchant generally lasts from 1 second to 5minutes, preferably from 3 seconds to 80 seconds, more preferably from 5seconds to 50 seconds.

The temperature during this surface treatment is generally from 20° C.to 100° C., preferably from 30° C. to 80° C., more preferably 50° C. to80° C.

During the surface treatment, the amount of removed aluminium of theclad outer layer side is 1 to 1000 mg/m² per side, preferably 5 to 500mg/m² per side, more preferably 5 to 300 mg/m² per side.

The aluminium alloy multi-layered brazing sheet material according tothe present disclosure has a typical thickness at final gauge in therange of about 0.05 mm to 4 mm, and preferably about 0.2 mm to 2 mm, andmore preferably about 0.2 mm to 1.5 mm.

In an embodiment, each covering clad layer has a thickness which isabout 0.5% to 10%, preferably 0.5% to 5%, of the entire thickness of themulti-layered brazing sheet, and each Al—Si brazing clad layer has athickness which is about 3% to 25%, preferably about 4% to 15%, of theentire thickness of the aluminium alloy multi-layered brazing sheet.

In an embodiment, the covering clad layer has a thickness in the rangeof 4 µm to 80 µm, preferably in a range of 5 µm to 50 µm.

It is important to keep the thickness of the covering clad layer thincompared to the thickness of the Al—Si brazing clad layer. The coveringclad layer has a thickness X₁ and the Al—Si brazing clad layer has athickness X₂ and the thickness ratio (X₂ to X₁) of the Al—Si alloybrazing clad layer and the covering clad layer is 2 or more to 1. In anembodiment the thickness ratio is 2.5 or more to 1, and preferably X₂ ≥3X₁, for example the thickness ratio is 2.5 to 1, or 3 to 1, or 3.5to 1. In some cases, the thickness ratio is represented by 2X₁<X₂<2.5X₁.

Preferably the total of the thicknesses of the covering clad layer andthe Al—Si brazing clad layer applied on a side of the core alloy layerare in a range of about 5% to 25%, preferably 5% to 15%, of the entirethickness of the multi-layered brazing sheet material.

In an embodiment of the present disclosure, the aluminium alloymulti-layered brazing sheet material is provided in an O-temper, andwhich is fully annealed.

In an embodiment of the present disclosure, the aluminium alloymulti-layered brazing sheet material is provided in a H3x-temper,H2x-temper or H1x-temper, and wherein x is 1, 2, 3, 4, 5, 6, 7 or 8,such as for example the H14, H18, H22, H24 and H26 temper.

As a particular example the aluminium alloy multi-layered brazing sheetmaterial is provided in an H14, H22, H24, or O-temper.

In a further aspect of the present disclosure, it relates to the use ofthe aluminium alloy multi-layered brazing sheet material or product forthe production by means of a flux-free controlled atmosphere brazing(CAB) operation of a heat exchanger, e.g. of a motor vehicle, and assuch, the aluminium alloy multi-layered brazing sheet material issuitable for being applied in heat exchangers for powertrain and enginecooling radiators, low temperature radiators, direct air-to-air chargeair cooling (“CAC”) or intercooling, air-to-water CAC, water-to-air CAC,air-to-refrigerant CAC, refrigerant-to-air CAC, air-to-refrigerantevaporators, air-to-refrigerant condensers, water-to-refrigerantevaporators, water-to-refrigerant condensers, heater cores, exhaust gascooling, exhaust gas recirculation systems, hybrid cooling system,two-phase cooling systems, oil coolers, fuel coolers, material forbattery cooling systems, chillers, cold plates, heat recovery systems,etc.

In a further aspect of the present disclosure there is provided anarticle comprising at least two formed members, for example formed bymeans of bending, folding, tube forming or deep drawing, joint to eachother in a flux-free controlled atmosphere brazing (CAB) operation, inparticular a heat-exchanger of a motor vehicle, incorporating at leastthe aluminium alloy multi-layered brazing material according to thepresent disclosure as one of the formed members.

In another aspect of the present disclosure there is provided a methodof manufacturing an assembly of brazed components, comprising the stepsof, in that order:

-   (a) providing or forming the components of which at least one is    made from an aluminium alloy multi-layered brazing sheet product as    herein set out or claimed; and preferably the multi-layered brazing    sheet is treated with an alkaline or acidic etchant;-   (b) assembling the components into an assembly; and preferably one    side of the multi-layered brazing sheet of the present disclosure    having the covering clad layer is being kept inside the assembly    forming the brazing sheet to constitute a structure, preferably a    hollow structure;-   (c) brazing the assembly without applying brazing flux in an inert    gas atmosphere, e.g. argon or nitrogen, at a brazing temperature,    typically at a temperature in a range of about 540° C. to 615° C.,    for example at about 590° C. or at about 600° C., for a period long    enough for melting and spreading of the Al—Si brazing material, for    example a dwell time of about 1 to 10 minutes, preferably 1 to 6    minutes, typically at around about 2 or 4 minutes, to form a fillet    between the filler material and at least one other component; and    wherein the oxygen content of the dry inert gas atmosphere is    controlled to a level as low as possible, preferably below 200 ppm,    and more preferably below 100 ppm, and more preferably below 40 ppm;    and-   (d) cooling of the brazed assembly, typically to below 100° C.; e.g.    to ambient temperature.

Ideally, when assembling the components into an assembly suitable forjoining by brazing, one side of the multi-layered brazing sheet productof the present disclosure having the thin covering clad layer is beingkept inside the assembly forming the brazing sheet to constitute astructure. While using the brazing sheet product according to thepresent disclosure there is no requirement to apply a brazing flux inorder to obtain a good joint following the brazing operation.

In a preferred embodiment the brazing inert gas atmosphere during thebrazing operation should be dry, meaning that the dew point is less thanminus 40° C., and more preferably of minus 45° C. or even lower.

Exemplary arrangements of the aluminium alloy multi-layered brazingsheet product 4, according to the present disclosure, are illustratedwin FIGS. 1A and 1B. A covering clad layer 2 and an Al—Si alloy brazingclad layer 1 can be applied on both sides or on one side only of a corelayer 3 and wherein the covering clad layer 2 forms the outer-layer ofthe aluminium alloy multi-layered brazing sheet product. When both sidesare clad, the multi-layered brazing sheet product has five layersincluding the core alloy layer as shown in FIG. 1A. When one side isclad with the brazing material, the multi-layered brazing sheet producthas a three-layer configuration as shown in FIG. 1B.

FIG. 2 is an isometric view of a portion of a brazed heat exchangerassembly. As shown in FIG. 2 , a brazed aluminium heat exchanger 12 inaccordance with the present disclosure may include a plurality offluid-carrying tubes 6 made from the multi-layered brazing sheet. Theends of the fluid-carrying tubes 6 are open to a header plate 8 and atank 10 (one end of the fluid-carrying tubes 6, one header plate 8 andone tank 10 are shown in FIG. 2 ). Coolant is circulated from the tank10, through the fluid-carrying tubes 6 and into another tank (notshown). As shown, a plurality of cooling fins 7 are disposed between thefluid-carrying tubes 6, in order to transfer heat away therefrom therebyfacilitating a heat exchange cooling the fluid therein.

ILLUSTRATIONS

Illustration 1 is an aluminium alloy multi-layered brazing sheet productfor brazing in an inert-gas atmosphere without a flux, comprising a corelayer made of a 3××× alloy comprising <0.20 wt.% Mg, and provided with acovering clad layer comprising 2 wt.% to 6 wt.% Si on one or both sidesof said 3××× alloy core layer and a Al—Si brazing clad layer comprising7 wt.% to 13 wt.% Si positioned between the 3××× alloy core layer andthe covering clad layer, wherein the covering clad layer has a thicknessX₁ and the Al—Si brazing clad layer has a thickness X₂ and wherein X₂ ≥2X₁.

Illustration 2 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the 3××× alloy corelayer comprises up to 0.1% Mg.

Illustration 3 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the covering cladlayer is Bi-free and Li-free.

Illustration 4 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the covering cladlayer is Mg-free, Bi-free and Li-free, and comprises, in wt.%,

Si 2% to 6%; Fe up to 0.5%; Mn up to 0.2%; Cu up to 0.1%; Zn up to 0.4%;Ti up to 0.1%; inevitable impurities, each <0.05%, total <0.15%, balancealuminium.

Illustration 5 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the covering cladlayer has a Si content in the range of 2.5% to 5%.

Illustration 6 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the 3××× alloy corelayer comprises, in wt.%,

-   0.5% to 1.8% Mn;-   <0.20% Mg;-   up to 1.1% Cu;-   up to 0.7% Si;-   up to 0.7% Fe;-   up to 0.3% Cr;-   up to 0.3% Sc;-   up to 0.3% Zr and/or V;-   up to 0.25% Ti;-   up to 1.7% Zn;-   unavoidable impurities each up to 0.05% and total up to 0.2%, and    balance aluminium.

Illustration 7 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the 3××× alloy corelayer has a Cu content up to 0.15%.

Illustration 8 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the 3××× alloy corelayer has a Cu content in the range of 0.15% to 1.1%.

Illustration 9 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the 3××× alloy corelayer has a Cu content in the range of 0.20% to 0.9%.

Illustration 10 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the Al—Si brazing cladlayer comprises, in wt.%,

Si 7%-13%, Mg up to 0.5%; Fe up to 0.7%; Cu up to 0.3%; Mn up to 0.8%;Zn up to 2%; Bi up to 0.3%; Ti up to 0.25%; balance aluminium andunavoidable impurities each <0.05%, total <0.2%.

Illustration 11 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the Al—Si brazing cladlayer has a Si content of 10% to 13%

Illustration 12 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the Al—Si brazing cladlayer has a Mg content of 0.02% to 0.5%

Illustration 13 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the Al—Si brazing cladlayer has a Bi content of 0.06% to 0.3%.

Illustration 14 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the multi-layeredbrazing sheet is surface treated with an alkaline or acidic etchantbefore a brazing step.

Illustration 15 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein the covering cladlayer has a thickness X₁ and the Al—Si brazing clad layer has athickness X₂ and wherein X₂ ≥ 2.5X₁.

Illustration 16 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein X₂ ≥ 3X₁.

Illustration 17 is the multi-layered brazing sheet product according toany preceding or subsequent illustration, wherein at least one of thecore layer, the Al—Si brazing clad layer, or the covering clad layercomprises at least 0.05 wt.% Ti.

Illustration 18 is a process for the production of a braze heatexchanger, comprising the steps of: providing at least one aluminiumalloy multi-layered brazing sheet product according to any of thepreceding or subsequent examples; and brazing in a flux-free controlledatmosphere brazing (CAB).

Illustration 19 the process according to any of the preceding orsubsequent illustrations wherein the multi-layered brazing sheet issurface treated with an alkaline or acidic etchant before a brazingstep.

Illustration 20 is use of an aluminium alloy multi-layered brazing sheetproduct according to any of the preceding illustrations in a flux-freecontrolled atmosphere brazing (CAB) operation to produce a heatexchanger apparatus.

All patents, publications and abstracts cited above are incorporatedherein by reference in their entireties. Various embodiments of thepresent disclosure have been described in fulfilment of the variousobjectives of the present disclosure. It should be recognized that theseembodiments are merely illustrative of the principles of the presentdisclosure. Numerous modifications and adaptions thereof will be readilyapparent to those skilled in the art without departing from the spiritand scope of the present disclosure as defined in the following claims.

1. An aluminium alloy multi-layered brazing sheet product for brazing inan inert-gas atmosphere without a flux, comprising: a core layer made ofa 3xxx alloy comprising<0.20 wt.% Mg, and provided with a covering cladlayer comprising 2 wt.% to 6 wt.% Si on one or both sides of said 3xxxalloy core layer and a Al—Si brazing clad layer comprising 7 wt.% to 13wt.% Si positioned between the 3xxx alloy core layer and the coveringclad layer, wherein the covering clad layer has a thickness X₁ and theAl—Si brazing clad layer has a thickness X₂ and wherein X₂ ≥ 2X₁.
 2. Themulti-layered brazing sheet product according to claim 1, wherein the3xxx alloy core layer comprises up to 0.1% Mg.
 3. The multi-layeredbrazing sheet product according to claim 1, wherein the covering cladlayer is Bi-free and Li-free.
 4. The multi-layered brazing sheet productaccording to claim 1, wherein the covering clad layer is Mg-free,Bi-free and Li-free, and comprises, in wt.%, Si 2% to 6%; Fe up to 0.5%;Mn up to 0.2%; Cu up to 0.1%; Zn up to 0.4%; Ti up to 0.1%; inevitableimpurities, each <0.05%, total <0.15%, balance aluminium.


5. The multi-layered brazing sheet product according to claim 4, whereinthe covering clad layer has a Si content in the range of 2.5% to 5%. 6.The multi-layered brazing sheet product according to claim 1, whereinthe 3xxx alloy core layer comprises, in wt.%, 0.5% to 1.8% Mn; <0.20%Mg; up to 1.1% Cu; up to 0.7% Si; up to 0.7% Fe; up to 0.3% Cr; up to0.3% Sc; up to 0.3% Zr and/or V; up to 0.25% Ti; up to 1.7% Zn;unavoidable impurities each up to 0.05% and totalup to 0.2%, and balancealuminium.


7. The multi-layered brazing sheet product according to claim 6, whereinthe 3xxx alloy core layer has a Cu contentup to 0.15%.
 8. Themulti-layered brazing sheet product according to claim 6, wherein the3xxx alloy core layer has a Cu content in the range of 0.15% to 1.1%. 9.The multi-layered brazing sheet product according to claim 6, whereinthe 3xxx alloy core layer has a Cu content in the range of 0.20% to0.9%.
 10. The multi-layered brazing sheet product according to claim 1,wherein the Al—Si brazing clad layer comprises, in wt.%, Si 7%-13%; Mgup to 0.5%; Fe up to 0.7%; Cu up to 0.3%; Mn up to 0.8%; Zn up to 2%; Biup to 0.3%; Ti up to 0.25%; balance aluminium and unavoidable impuritieseach <0.05%, total <0.2%.


11. The multi-layered brazing sheet product according to claim 10,wherein the Al—Si brazing clad layer has a Si content of 10% to 13%. 12.The multi-layered brazing sheet product according to claim 10, whereinthe Al—Si brazing clad layer has a Mg content of 0.02% to 0.5%.
 13. Themulti-layered brazing sheet product according to claim 10, wherein theAl—Si brazing clad layer has a Bi content of 0.06% to 0.3%.
 14. Themulti-layered brazing sheet product according to claim 1, wherein themulti-layered brazing sheet is surface treated with an alkaline oracidic etchant before a brazing step.
 15. The multi-layered brazingsheet product according to claim 1, wherein the covering clad layer hasa thickness X₁ and the Al—Si brazing clad layer has a thickness X₂ andwherein X₂ ≥ 2.5X₁ _(.)
 16. The multi-layered brazing sheet productaccording to claim 15, wherein X₂ ≥ 3X₁ _(.)
 17. The multi-layeredbrazing sheet product according to claim 1, wherein at least one of thecore layer, the Al—Si brazing clad layer, or the covering clad layercomprises at least 0.05 wt.% Ti.
 18. A process for the production of abraze heat exchanger, comprising the steps of: providing at least onealuminium alloy multi-layered brazing sheet product according to claim1; and brazing in a flux-free controlled atmosphere brazing (CAB). 19.The process of claim 18, wherein the multi-layered brazing sheet issurface treated with an alkaline or acidic etchant before a brazingstep.
 20. Use of an aluminium alloy multi-layered brazing sheet productaccording to claim 1 in a flux-free controlled atmosphere brazing (CAB)operation to produce a heat exchanger apparatus.